Senator Deirdre de Burca today resigned from the Green Party and the Seanad with immediate effect.

Ms de Burca announced she could no longer continue to support the Greens in government and revealed she had lost confidence in party leader John Gormley.

In a letter to Mr Gormley, the senator accused him of having done a disservice to the party and its members in allowing a drift to occur.

"I regret to say that I can no longer support the Green Party in government as I believe that we have gradually abandoned our political values and our integrity and in many respects have become no more than an extension of the Fianna Fail party," she said.

A spokesman for the Green Party said they were aware of the resignation and would respond in due course.

"It is disappointing but not unexpected," he added.

Ms de Burca has served as an elected member of the Green Party for eight years on Wicklow County Council and for a further two and a half years as a member of Seanad Eireann. The politician failed to win a seat as an MEP in the last European Elections.

Shock

Ms de Burca's resignation is the second shock departure from Irish politics this week.

On Monday journalist turned politician George Lee announced he was quitting the Dail less than nine months after being elected.

The Dublin South TD, who won the seat for Fine Gael last June, said he was stepping down because he has had little impact on the opposition party's economic policies.

Ms de Burca accused Mr Gormley of not being able to take a stronger line with Taoiseach Brian Cowen and his Fianna Fail party, who she claimed were not cooperating in implementing policy initiatives agreed in the Programme for Government.

"From stonewalling us and trying to unravel key aspects of our policy initiatives being implemented, to ignoring our input into the preparation of new legislation, to reneging on two key agreements made between party leaders, the Fianna Fail party continues to 'run rings' around us and to take advantage of our inexperience and our very obvious fear of facing the electorate," she continued in her letter of resignation.

Lost

Ms de Burca said it appeared holding on to office and seats had become more important to the party than holding on to its fundamental political purpose.

"We have lost our way as a party and I am sad to say that it has reached a point where I, and most of the people I know, will be unable to vote Green in the next election," she added.

The Green Party leadership has faced severe criticism from its members and supporters since it entered into a coalition government in 2007.

Just over a year ago three councillors quit amid claims of a growing split between the leadership and grassroots.

When Letterkenny town councillor Neil Clarke resigned in December 2008 he said he had become disillusioned with the party chiefs and felt he could not go before voters again as a Green.

Within weeks, Cork city councillor Chris O'Leary and Dublin representative Bronwen Maher left the party.

Mr O'Leary, who had been one of the most senior party figures in Munster, said he believed the Greens had followed a "stay in government at all costs" agenda.

Ms Maher accused the leadership of unethical conduct and criticised its failure to speak out at Budget cuts.

Discomfort

Ms deBurca said she had several conversations with Mr Gormley about her growing discomfort with the decisions the Green Party has been supporting in government.

"You have been very aware of my frustration with the fact that despite the Green Party holding the balance of power in this government for some time now, our willingness to try to exercise that influence appears to grow less with every passing week," she wrote.

"As a party, we seem to have been paralysed by the electorate's rejection of many of our candidates (including myself) in the local and European elections last June.

"Any suggestion that we challenge Fianna Fail, or face it down over important issues, seems to bring up a great fear in us that we will have to leave government.

"In fact staying in government appears to have become an end in itself now for the Green Party.

"While I was always aware that our political inexperience as a party would leave us vulnerable to being manipulated by Fianna Fail in government, what I hadn't predicted was the strong attachment to office that appears to have developed since we became part of government."

United

Green TD and senators issued a joint statement insisting the parliamentary party was united.

"We are disappointed by Deirdre's decision. We are aware that she has been unhappy with her situation for some time," the party said.

"The parliamentary party is totally united. We will continue to operate in a collegiate way.

"The Green Party is about implementing progressive policies and improving our society. We are serving in government at a critical time for the country, and we have made tough choices that are vital to the peoples' interests.

"In government we have brought about huge changes in Ireland's energy, planning and enterprise policies.

"In recent months we have introduced civil partnerships legislation, a levy on carbon and a major programme of political reform, including a directly elected mayor for Dublin this year. Our policies have created tens of thousands of new, valuable jobs."

The Greens said they would reconsider their role in government if they felt no progress was being made.

"Our position has remained the same since entering government in June 2007. We have come to do a job and as long as we are getting that job done we will stay. If we are not making progress, we will think again," the party said.

"Eight out of 10 of our members backed that view in 2007 when they endorsed the party's entry into government. Precisely the same number again backed that view in October 2009 when they were presented with the Renewed Programme for Government."